Semiconductor devices generate heat during their operation, and this heat usually acts to degrade the operation of the semiconductor device. For power semiconductor devices it is necessary to be cooled during operation to maintain acceptable device performance, and for high power semiconductors liquid cooling is often applied.
U.S. Pat. No. 5,269,372 describes a cold plate for cooling power modules. Liquid is let through an inlet to a chamber, in which a manifold distributes the liquid through several holes into a cooling plate exhibiting inlet conduits and return conduits. The plate, preferably manufactured in copper, is divided into a 6×6 cubicle matrix. Between each two cubes, a fluid channel connects an inlet conduit and a return conduit. This solution achieves a reduction in the temperature gradient, but is expensive due to the need for a heat conducting cold plate. Making a cooling construction which avoids the necessity of a cold plate thus is of interest. Further, due to narrow channels and inlets, the flow resistance is high, thus limiting an increase in cooling capacity.
U.S. Pat. No. 5,841,634 discloses a liquid-cooled semiconductor device, like the one this invention relates to. The semiconductors are here placed inside a housing on a wall, which is to be cooled. The device shows a fluid inlet port and a fluid outlet port, and a baffle placed in a chamber inside the housing. The baffle includes a wall separating the chamber into a top- and a bottom portion, and walls separating each portion into compartment. A number of holes in the wall between top- and bottom portion provide fluid communication between the portions. Fluid is let from the inlet port to a first bottom compartment, and then through holes to a first top compartment. In the top compartment the fluid is let along the wall, which is to be cooled, and through holes to a second bottom compartment. From the second bottom compartment the fluid is let to a second top compartment, where it cools another area of the wall, which is to be cooled. After having passed three top compartments the fluid it let to the fluid outlet port, and out of the device. Thus the cooling compartments of the device is connected in a serial manner.
As the fluid passes the first top compartment, the cooling effect from the fluid will have lead to a higher outlet temperature than the inlet temperature. When the fluid then reaches the second top compartment, additional heating of the fluid will take place, and this will lead to a temperature difference on the cooled wall, from fluid inlet port end to fluid outlet port end. As high power semiconductors are very sensitive to temperature variations, and also sensitive to the temperature level, equal cooling conditions for all semiconductors in a power semiconductor device will have a large impact on the lifetime for the device.
Also the serial connection of multiple cooling compartments will have a high flow resistance as a result, leading to a high pressure drop or a low flow rate of the fluid through the cooling device.
It is an object of this invention to improve the cooling conditions of a semiconductor device, whereby a more equal internal temperature is obtained.
It is a further object of this invention to reduce the flow resistance, whereby the flow rate will increase, leading to a higher cooling capacity.